I own a 1993 dakota 4x4 with a 5.2 v-8, auto with 3.55 rear end. My question is my truck's standard tires is 215R75-15 and I went with 30x9.50- 15 tires. My son owns a 1997 dakota with the same drivetrain that I have. He is running 31 series tires. My gas mileage dropped to around 13-14 mpg and my low end went out the window. My sons truck will run circles around mine and gets around 17 mpg. Is the final drive/ratio different between the two trucks??

 

The 92-95 V8's had the 46rh. The 46RH Four speed (V8 only) has theses gears 1st 2.45, 2nd 1.45, 3rd 1.0, 4th 0.69, Rev. 2.21. This was in the FAQ in this section.

The 97-up 5.2 on the Dakota came with the 44re. 44RE has 2.740 1.540 1.000 0.690

http://www.vibratesoftware.com/html_...nsmissions.htm

If you went with a taller tire, but you didn't change the ring and pinion ratios you will get poor MPG and power, like you are feeling. Also your speedometer and odometer will be incorrect since it is a taller tire.

 

if i remember right the rear end gear, 3.55 X the lowest gear in the trans 2.74 gives 9.72 final drive. 3.55 X 0.69 O.D. = 2.44 my 2001 dak V6 3.9, 4.1 rear end gear X 2.72 = 11.23. my dak was 3.55 rear end, i was getting 8-9 MPG. i drive hard. went to 4.1. my MPG went to 11-12. why? cause it let my trans go into O.D. at 35 MPH. most of my driving is 35- 45 MPH. if i drove on the hi way iam sure my MPG would go down